Miller’s chemico-parasitic theory is still the best explanation of the etiology of caries. When human saliva is mixed with sugar-broth, or saliva containing carbohydrate-food debris is subjected to acid fermentation, the pH generally attains values between 4.0-5.5—acid enough to attack enamel. When dog saliva is mixed with sugar-broth, acidification does not occur, but the ensuing pH is in the alkaline range. Dogs are immune to caries ; lactobacilli do not live in their mouths.
‘The mouths of most persons contain lactobacilli that are Gram-positive, non- motile, non-spore-forming highly-variable rods which grow in S and R forms. Attempts strictly to differentiate these inhabitants of human mouths and intestines have been unsuccessful. Human saliva influences the surface of the tooth. Mineral salts dissolved from enamel can be restored under experimental conditions. Evaluation of the existing dissimilarities in fermentative qualities of different salivas, the solubilities of enamel in weak acids, the varying mineralizing power of saliva—and the significance of each—need further study.
Reference: Bull. lInd Stom. Cong., 1935.